I was impressed with GMail's Auto-unsubscribe feature after noticing it today. Let's say you spotted in your GMail inbox, a newsletter that you are no longer interested in or a message from a list group that you don't remember subscribing to. When you mark such a message as spam by clicking on the "Report Spam" button, you may see a dialog box that asks if you want to report spam as well as Unsubscribe from that list.
Once you click on it, GMail will send a request to the sender on your behalf that your email address be removed from the list. The Unsubscribe option is not available though for all mailing lists and this option won't be shown for lists that are known to be owned by spammers.
You can try a bunch of other similar tricks by going to the Gmail Labs feature from the Settings link that's at the top right corner after you are logged in.
Also see:
A Spooky (but fun) incident with GMail
HOW TO fetch unread emails from a mail server
HOW TO send an email programmatically using C# with GMail
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